Time-temperature dosimeter

ABSTRACT

The present disclosure relates to a dosimeter for measuring exposure to heat over time in combination with peak temperature indicators and reversible temperature indicators. The preferred temperature indicator tag is credit card sized and comprises four time-temperature dosimeters. Each dosimeter has a wick in contact with a separate reservoir containing a mix of a colored dye, a wax and an amorphous polymer to indicate a distinct temperature range when the mix melts. The wicks are preferably made of porous paper with a pore size around 8 microns to allow for proper capillary action along its length. An adhesive, except where each wick contacts its respective reservoir and at a vent, preferably seals each wick. The tag preferably has a plurality of peak temperature indicators where each indicator has a blend of a dye, a wax and a polymer for a temperature indication range. The tag also preferably has a plurality of reversible temperature sensors.

This invention was made with government support under (W15QKN-09-C-0153)awarded by U.S. Army JML Contracting Center. The government has certainrights in the invention.

FIELD

The present disclosure relates to a dosimeter for measuringtime-temperature exposure in combination with peak temperatureindicators and reversible temperature indicators.

BACKGROUND

A number of different types of time-temperature and heat detectiondevices exist. However, these devices are often not able to effectivelymeasure the total time of exposure to predetermined temperature levels;have limited product life spans; and/or have temperature ranges that aretoo limited for particular applications. Accordingly, a device is neededthat can more effectively measure exposure to temperature over time,over an extended product life span and with a greater temperature range.

SUMMARY OF THE INVENTION

The present disclosure relates to a dosimeter for measuring exposure toheat over time in combination with peak temperature indicators andreversible temperature indicators. The preferred temperature indicatortag is credit card sized and comprises four time-temperature dosimeters.Each dosimeter has a wick in contact with a separate reservoircontaining a mix of a colored dye, a wax and an amorphous polymer toindicate a distinct temperature range when the mix melts. The wicks arepreferably made of porous paper with a pore size around 8 microns toallow for proper capillary action along its length. An adhesive, exceptwhere each wick contacts its respective reservoir and at a vent,preferably seals each wick. The tag preferably has a plurality of peaktemperature indicators where each indicator has a blend of a dye, a waxand a polymer for a temperature indication range. The tag alsopreferably has a plurality of reversible temperature sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention described herein will become apparent from thefollowing detailed description considered in connection with theaccompanying drawings, which disclose several embodiments of theinvention. It should be understood, however, that the drawings aredesigned for the purpose of illustration and not as limits of theinvention.

FIG. 1 is a front perspective view of a preferred embodiment of theinvention;

FIG. 2 is an exploded perspective view of a preferred embodiment of theinvention; and,

FIG. 3 is an exploded perspective view of a preferred embodiment of apeak temperature indicator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Various embodiments are now described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of one or more embodiments. It may be evident however,that such embodiment(s) may be practiced without these specific details.

In the following paragraphs, the present invention will be described indetail by way of example with reference to the attached drawings.Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention. As used herein, the “present invention” refers to anyone of the embodiments of the invention described herein, and anyequivalents. Furthermore, reference to various feature(s) of the“present invention” throughout this document does not mean that allclaimed embodiments or methods must include the referenced feature(s).

Referring now to FIG. 1, a perspective front view of a preferredembodiment of the invention 10 is shown. The embodiment shown in FIG. 1is a temperature indicator tag 10, preferably credit card-sized, with aset of four time-temperature dosimeters 20, a set of four reversibletemperature sensors 30, and a set of four peak temperature indicators40. The reversible temperature sensors 30 preferably comprise liquidcrystal temperature indicators such as those made by TMC Hallcrest. Thedosimeters 20 are preferably configured to indicate a time-temperatureindication period of 500 hours at 160 degrees Fahrenheit or more. Eachdosimeter 20 preferably has a wick 22 below a transparent plastic film50. Each wick 22 is preferably, approximately 2 inches in length. Thepreferred wick medium is paper, e.g. Whatman 2, having a pore size ofapproximately 8 microns. However, a range of 2-30 microns is usable.Furthermore, other porous wick media that can withstand heat-sealingtemperatures such as glass fiber paper may be used.

It should be noted that “wicking” starts fast and slows as wickedsubstance proceeds along a generally constant width and depth wick. Therate of slowing can be modulated by tapering the wick in the directionof travel. For a larger taper, a lower rate of slowing can be achieved.A decreasing non-linear wick taper such as an exponential or power curveshape may result in a more linear wicking rate over time compared to alinearly decreasing taper. Conversely, a wick that tapers such that itincreases in size in the direction of travel can slow the rate ofwicking over that of a non-dimensionally changing wick. For the presentinvention, the wicks 22 could be untapered. However, preferably thewicks 22 start out ⅛″ wide with a 5:1 taper that provides an end pointof 0.025″. A larger taper would likely be more difficult to see if itnarrowed to a width less than 0.025″. Preferably, a tapered wick wouldbe no smaller than 0.025″ at the taper end. If the wick 22 started witha wider end, it would allow larger tapers that can be more easilyvisualized for ease of use and readability.

Referring now to FIG. 2, a perspective exploded view of a temperatureindicator tag 10 is shown. A transparent or clear film 50 covers a frontside of the set of four wicks 22 for the time-temperature dosimetershown. A time-temperature scale can be printed on plate 50 as shown inFIG. 1. The film or plate 50 is preferably thermoplastic polycarbonate.An opaque film or plate 60 covers the back side of the wicks 22. Theplate 60 is also preferably thermoplastic polycarbonate.

As shown in FIG. 2, there is preferably a set of four reservoirs 80where each reservoir preferably contains a blend of a crystallinemelting material such as wax, a polymer and a colored dye. The waxesused are narrow melting range paraffin waxes known as thermostat waxesas they are typically used for this industrial application. A typicalformula would be 39.75% HA-20 (a 100° F. melting wax from IGIInternational), 60% Oppanol® B 10 SFN (a 40, 000 MW polyisobutyleneresin from BASF), and 0.25% Blue R3 (a solvent dye from ColorChemInternational). Below is a table of preferred wax-polymer-dye blends foruse in the dosimeters:

100 MP TT 60% B10 BASF 39.75% HA20 IGI 0.25% Blue R3 Blend polymer waxColorChem 130 MP TT 65% B10 BASF 34.75% HA26 IGI 0.25% Green B5 Blendpolymer wax ColorChem 160 MP TT 67% B10 BASF 32.75% 150 model 0.25%Violet BV Blend polymer IGI wax ColorChem 190 MP TT 70% B10 BASF 29.75%180 model 0.25% Red PS Blend polymer IGI wax ColorChem

The wax-polymer-dye mixes/blends are preferably mixed together by highshear mixing and elevated temperature heating, e.g. 50-100 degreesFahrenheit above the melting point of the wax used in the blend, to forma single blended mixture that does not separate. The mixture ispreferably then filtered to remove non-blended polymer gels. It shouldbe noted that even a small amount of polymer gel could preferentiallyattach to wicking media and slow the wicking rate of the polymer-wax-dyeblend. The mix operates such that when the wax is below its meltingpoint, it is a solid that locks the extremely high viscosity liquidpolymer, e.g. polyisobutylene, from moving. When the blended wax meltsthe polymer resin flows and wicking can proceed along the length of thewick via capillary action thus indicating a particular time-temperaturedose. Alternative low crystallinity polymers such as amorphouspolypropylene or amorphous polyolefins may also be used. Ultra lowcrystallinity polymers used for slowing wicking rates are preferred.They allow formulation of blends that flow when the crystalline nonpolymer melts. A typical formula is a low molecular weight amorphouspolymer 60-70%, wax 30-39.75%, and dye 0.25%. The mixture melting pointis determined by the melting point of the wax that is selected. Mixtureratios are chosen for their viscosity that determines travel within afixed wick path length of 1-3 inches over a 1000-hour time frame.

The bonding of the layers is an integral component of the invention asfailure in the bonding of the layers could cause a failure in thetime-temperature wicking rate. The most critical bond is the bondbetween the wicks 22 and the clear film 50 and the opaque film 60. Thewicks 22 need to be sealed without gaps (except for the contact points62 with reservoirs 80 and the vent 64 at the end of the wick 22 oppositethe reservoir 80) in order that wicking may proceed in a measured rate.An improper gap can cause wicking to occur at a faster rate than isintended. The improper gap can also cause excess material to collect insuch a gap. A sealing adhesive is needed to seal the wicks 22 and toadhere the films 50, 60, 70 and 90 together. However, it is preferablethat the sealing adhesive not penetrate the wicks 22 more thansuperficially so that the wicking pores are not clogged and interferewith the flow of the blends along the wicks 22. A sealing adhesive forthe purpose of this invention is a plastic whose heat deflectiontemperature is above the invention's intended use temperature but belowhigher temperature backing film.

In addition, the sealing adhesive preferably thermally deforms aroundthe wick 22 edges so as not to allow a void to form on the wick 22.During heat-sealing, plastics soften and flow. Accordingly, duringheat-sealing, the clear film 50, the wicks 22 and opaque film 60 can befitted into a mold to prevent dimensional changes from occurring duringthe heat sealing process. The reservoir plate 70 contains internalfeatures and preferably should have a mold with male internalprojections corresponding to the internal cut outs during heat sealing.For high-speed lamination, a mold-less process is preferred. To reducethe incidence of dimensional shift during heat-sealing of the plasticfilms 50, 60, 70 and 90, it is preferable that a lower temperaturemelting adhesive plastic film, such as polycarbonate-polyester alloy, islaminated to a higher temperature melting plastic film, such aspolycarbonate.

Preferably, the sealing adhesive should not penetrate the wicks 22 morethan superficially during heat sealing or during elevated temperatureusage of the invention. The sealing adhesive preferably does notchemically interact with the mixes in the reservoir 80 as this mightreduce the adhesive bonding between the device components. The sealingadhesive preferably has a heat deflection temperature greater than theuse temperature of the device 10 to maintain bonding strength. Thesealing adhesive's crystalline melting temperature is preferably greaterthan the heat-sealing temperature in order that the wicks 22 not becompletely penetrated. The preferred adhesive film is polycarbonateblended with a low crystallinity thermoplastic polyester.

The reservoir plate 70 is preferably heat sealed to the back of theopaque film 60. The reservoirs 80, e.g. paper/sponges containing thepreferred wax-polymer-dye blends, are placed in the reservoir plate 70.The vent plate 90 preferably provides pressure venting for the wicks 22via the vent channel 92 aligned with vent 64 on the opaque film 60. Thevent plate 90 is sealed to the back of the reservoir plate 70. In turn,the vent channel 92 on plate 90 is aligned with the vent hole 110 on theback plate 100. Thus, the vent 64, vent channel 92 and vent hole 110work in combination to vent pressure between the reservoirs 80 andwicking media 22 and the environment. The peak temperature indicators 40and current temperature indicators 30 are placed into the reservoirplate 70. The back plate 100 is preferably sealed to the back of thevent plate 90 using pressure sensitive adhesive, e.g. 3M 467. Duringheat sealing, the clear/transparent film 50, the wicks 22 and the opaquefilm 60 are heated to around 300° F. and are compressed together with aforce between 100 and 1000 psi to cause the plastic to soften and allowbonding to occur. The plastic of the films 50 and 60 and the sealingadhesive mold around the wicks 22 so that negligible gaps are present(except where the wicks contact the reservoirs 80, namely the reservoircontact point 62). Small gaps in the sealing adhesive on the wicks 22 ofa few thousandths of an inch or greater could cause internal floodingwhich would affect the accuracy of the device 10.

Each reservoir 80 is preferably vented to relieve positive and negativepressure that would occur if the reservoirs 80 were sealed and theambient pressure/pressure exterior to the device 10 rose or fell.Additionally, during use when the wax-polymer mixture in the reservoirs80 melt, the wax undergoes an expansion that can tend to pressurize thereservoirs 80. The time-temperature device accuracy is improved whenthere are only small pressure effects to cause the wicking rate toeither speed up during a pressure rise in the reservoirs 80 and likewiseto slow down during a pressure fall in the reservoirs 80. The pressureeffects are changes relative to the external or ambient pressure, inessence the gauge pressure that takes into account absolute pressure andadds or subtracts from this pressure. For optimal device function, thereservoir gauge pressure should be zero. If the device 10 were placed ina vacuum, it could still function correctly as the external surface ofthe device pressure should still be the same as the internal reservoirpressure. Blockage of one or more of the reservoirs 80 when thewax-polymer-dye mixture melts would result in pressure in the reservoirbeing higher than the outside environment.

Referring now to FIG. 3, a preferred embodiment of a set of four peaktemperature indicators 40 is shown. Reference number 44 refers to asponge/paper such as the reservoirs 80 shown in FIG. 2—preferably aWhatman paper having porosity between 2 and 30 microns. The peaktemperature indicators 40 preferably each comprise a reservoir chamber42 and a peak reservoir 44 containing a mix of a wax, polymer and dyebelow an opaque white porous wick 46 and a peak temperature indicatornumber 48, preferably a reverse white printed number corresponding tothe peak temperature to be indicated. The top layer of the peaktemperature indicators 40 are preferably white reverse printed numbers48 on clear plastic. The wicks 46 are preferably white paper squaresplaced below the numbers where the color of the wicks 46 match the whitecolor of the plastic numbers 48. When assembled the reverse printednumbers 48 are less readily visible. When each colored wax-dye mixture46 reaches its predetermined melting point, the colored circle mixture44 migrates to the adjacent white square 46 by capillary flow and thereverse white printed numbers 48 become easy to read as the white paper46 becomes colored. A critical aspect of the peak temperature indicatorsis they should react fairly quickly when the corresponding predeterminedpeak temperature has been reached. The colored-wax mixes in reservoir 44melts and it is absorbed into the porous paper 46 to reveal the reversepre-printed number corresponding to the peak temperature of interest. Asmall amount of polymer may be added to the wax to slow the action.Alternatively one could substitute a stencil cut number on a whiteplastic above the white paper to show the same effect as the reversewhite number on clear plastic. The preferred mixes stored in reservoirs44 for the peak temperature indicators 40 are a 94.75-99.75% wax 0-5%polymer, 0.25% dye mix. The following table shows a preferred set ofwax-polymer-dye mixes for use in peak temperature indicators:

115 MP Peak 5% B10 BASF 94.75% 2202A IGI 0.25% Blue R3 Blend polymer waxColorChem 145 MP Peak 5% B10 BASF 94.75% Astorstat 0.25% Green B5 Blendpolymer 10037 IGI wax ColorChem 175 MP Peak 5% B10 BASF 94.75% 174/175IGI 0.25% Violet BV Blend polymer wax ColorChem 190 MP Peak 5% B10 BASF94.75% 180 model 0.25% Red PS Blend polymer IGI wax ColorChem

Each reservoir chamber 42 containing the wick 46 and reservoir 44 withmix can be sealed in thin clear plastic bags with separate compartmentsto keep the colors from different reservoir chambers 42 from mixing.

Accordingly, the present invention can be used in a wide variety ofapplications such as food or medicine preservation or chemicalmonitoring, e.g. monitoring whether a particular substance has exceed apredetermined temperature for a predetermined period of time. Given thatwicking in the present invention can be kept to slow speeds or evenstopped and started again, monitoring times up to 500 hours and up aftera period of ten years are possible.

Various modifications and alterations of the invention will becomeapparent to those skilled in the art without departing from the spiritand scope of the invention, which is defined by the accompanying claims.It should be noted that steps recited in any method claims below do notnecessarily need to be performed in the order that they are recited.Those of ordinary skill in the art will recognize variations inperforming the steps from the order in which they are recited. Inaddition, the lack of mention or discussion of a feature, step, orcomponent provides the basis for claims where the absent feature orcomponent is excluded by way of a proviso or similar claim language.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that may be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features may be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations may be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein may be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead may beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of theinvention may be described or claimed in the singular, the plural iscontemplated to be within the scope thereof unless limitation to thesingular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether flow control or other components, may be combined in asingle package or separately maintained and may further be distributedacross multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives may be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1-5. (canceled)
 6. A time-temperature dosimeter with a predetermined usetemperature comprising: a transparent plastic film coated on one sidewith an adhesive with a heat deflection temperature greater than the usetemperature; a porous wick adhered to the film by the adhesive and incontact with a reservoir; the reservoir containing a crystalline meltingmaterial having a predetermined melt point and viscosity mixed with anamorphous polymer with a predetermined viscosity forming a blend wherethe blend viscosity is less than the polymer viscosity; and, an opaqueplastic film coated on one side with an adhesive film, the adhesive filmwith a heat deflection temperature greater than the use temperature,whereby the adhesive film is adhered to the wick.
 7. Thetime-temperature dosimeter of claim 6 where the wick is sealed by theadhesive except where the wick contacts the reservoir at a reservoircontact point.
 8. The time-temperature dosimeter of claim 6 where thecrystalline melting material is paraffin wax.
 9. The time-temperaturedosimeter of claim 6 where the amorphous polymer is polyisobutyleneresin.
 10. The time-temperature dosimeter of claim 6 where the blendfurther comprises a colored dye. 11-16. (canceled)
 17. A peaktemperature indicating device comprising: a mix of a colored dye, a waxand an amorphous polymer; an opaque porous wick; and, an opaque nonporous cover with a transparent number.
 18. A time-temperature dosimeterwith a predetermined use temperature comprising: a transparent highertemperature melting plastic film coated on one side with an adhesivewith a heat deflection temperature greater than the use temperature; aporous wick adhered to the film by the adhesive and in contact with areservoir; the reservoir containing a crystalline melting materialhaving a predetermined melt point and viscosity mixed with an amorphouspolymer with a predetermined viscosity forming a blend where the blendviscosity is less than the polymer viscosity; and, an opaque, highertemperature melting backing film bonded to a low crystallinitylaminating adhesive film with a heat deflection temperature greater thanthe maximum use temperature, whereby the laminating adhesive film isadhered to the wick and the laminating adhesive film seals the wick andwicking media.